The present invention relates to a pressure-limiting valve comprising a valve housing, a valve piston with a pressure-limiting spring, wherein the pressure-limiting valve is, in particular, a pressure-limiting valve of an air treatment system for a brake system for a utility vehicle.
Air treatment systems for pneumatic brake systems, in which a safety valve for a reduced-pressure circuit for a pressure limiter is integrated, are known in connection with utility vehicles.
The air treatment arrangement is a central component in a pneumatic brake system of a utility vehicle, in which air treatment arrangement the oil- and water-containing air which is delivered by the compressor is filtered and cleaned. The compressed air is allocated, at the required pressure and in the correct filling order, to the various brake circuits and air consumers in the utility vehicle. In the event of a defect, the individual brake circuits are secured in relation to one another, so that an adequate auxiliary braking effect is available for braking the utility vehicle (for example a heavy goods vehicle). An electronic air treatment arrangement contains, in addition to a control electronics system, sensors and actuators. The most recent air treatment devices additionally also contain an electronic parking brake (EPB).
In this case, some of these brake circuits operate at a relatively low pressure level which lies below the pressure level of the other brake circuits.
In this case, the pressure can be reduced to the desired low level using a pressure-limiting valve. Since the force of the spring of the pressure limiter is adjusted using an adjusting screw, the desired pressure level adjusted.
Different designs are known for pressure-limiting valves of this kind. The prior art discloses, in particular, pressure-limiting valves according to the “pushing shut” principle, in which, in the event of an increase in pressure in the system, the pressure limiter closes at the defined closing pressure and thereby limits the outlet-side pressure. In the event of a further increase in pressure on the inlet side of the pressure limiter, said pressure limiter is pushed shut by means of an active face on the valve and the sealing force at the valve seat increases. A pressure-limiting valve of this kind is known, for example, from DE 10 2010 947 491 A1.
Further pressure-limiting valves are known from DE 33 11 816 C1, DE 26 20 135 A1, DE 41 14 977 A1, DE 30 26 283 A1, DE 26 19 769 A1, DE 26 19 769 A1, DE 600 24 496 D2 and DE 20 2006 017 517 U1, wherein these valves likewise operate in accordance with the “pushing shut” principle.
A further principle for pressure-limiting valves is the “pulling shut” principle, wherein, in the event of an increase in pressure in the system, the pressure limiter closes at a defined closing pressure and thereby limits the outlet-side pressure. In the event of a further increase in pressure on the inlet side of the pressure limiter, an active face on the piston generates a force which is introduced into the valve seat as tensile force by the piston. The sealing force at the valve seat is increased as a result.
DE 43 44 416 A1 discloses a pressure-limiting device which operates in accordance with the “pulling shut” principle. However, this pressure-limiting valve does not have a safety valve function.
The object of the present invention is to advantageously develop a pressure-limiting valve of the kind outlined in the introductory part, in particular to the effect that it can be constructed with a lower installation space requirement and also with fewer components.
According to the invention, a pressure-limiting valve includes a valve housing, a valve piston and a pressure-limiting adjusting spring, wherein at least one valve inlet and at least one valve outlet are provided in the valve housing, wherein the valve piston can assume an open position, in which the valve inlet and the valve outlet are connected to one another, and at least one closed position, in which the valve inlet and the valve outlet are separated from one another, wherein the valve piston has a first piston ring with a sealing face and has a second piston ring, wherein, in the closed position, the sealing face of the first piston ring is pulled against a housing lip by a pneumatic force which acts on the second piston ring and which is directed against the force of the pressure-limiting adjusting spring, and wherein, furthermore, there is a pneumatic passage in the valve piston for the purpose of creating a safety valve function, as a result a spring-loaded safety valve body which is arranged on that side of the second piston ring which is opposite the valve outlet can be closed.
The invention is based on the basic idea that a safety valve function is integrated in the pressure-limiting valve. Owing to the integration of a safety valve function in the pressure-limiting valve, the pressure-limiting valve can be constructed in a more simple manner overall and as a result parts of the pressure-limiting valve and of the safety valve can be dispensed with. The pressure-limiting valve according to the invention is a pressure-limiting valve in accordance with the “pulling shut” principle which allows a self-reinforcing effect when a predefined closing pressure is exceeded. In the event of an increase in pressure in the system, the pressure limiter closes at the defined closing pressure and thereby limits the outlet-side pressure point. In the event of a further increase in pressure on the inlet side of the pressure limiter, an active face on the piston generates a force which is introduced into the valve seat as tensile force by the piston. As a result, the sealing force on the valve seat is increased and therefore has a self-reinforcing effect. Owing to the integration of the safety valve function, pressure from the pressure-limited circuits can be kept below a maximum defined permissible pressure in the event of a fault. If this pressure is exceeded, the spring-loaded safety valve body which is arranged in the pressure-limiting valve can open and release pressure in this way. The safety valve function is formed in this way.
Integrating the safety valve function in the pressure-limiting valve has the advantage that there is a lower installation space requirement since the safety valve is accommodated in the installation space of the pressure limiter.
Furthermore, it can be provided that the safety valve body is spring-loaded by the pressure-limiting adjusting spring. In this way, it is possible that a separate spring for the safety valve body is not required for forming the safety valve function by means of the safety valve body. As a result, some components can be saved, in particular the spring and also the adjusting screw of the safety valve. Costs can be saved in this way.
In addition, it is possible that the safety valve body has a guide which, in a closure position, is guided in a recess of the second piston ring. Guiding the safety valve body in a recess of the second piston ring can have the effect that the safety valve body performs a defined movement relative to the second piston ring and therefore to the valve piston. A robust design and a defined ability to adjust the closing characteristics are possible as a result.
Furthermore, it can be provided that the safety valve body bears on the second valve seat by way of a sealing face, and in this way closes the pneumatic passage in a sealing manner, at least in the closed position. As a result, a simple and small design of the pressure-limiting valve with the integrated safety valve function is possible and facilitated.
Furthermore, it can be provided that the limit pressure, at which the pressure-limiting valve switches to the closed position, can be adjusted by the pressure-limiting adjusting spring and an adjusting element. In particular, it is conceivable that the adjusting element is an adjusting screw. This allows simple and robust adjustment of the switching characteristics of the pressure-limiting valve.
In particular, it can be provided that the prestress of the pressure-limiting adjusting spring can be adjusted by the adjusting element.
Furthermore, it can be provided that the limit pressure, at which the safety valve body releases the pneumatic pressure, can be adjusted by the pressure-limiting adjusting spring and an adjusting element. The adjusting element may be the adjusting element of the pressure-limiting valve or the adjusting screw of the pressure-limiting adjusting spring for adjusting the prestress of the pressure-limiting adjusting spring.
Furthermore, it can be provided that the pneumatic passage is formed by a passage bore through the valve piston.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.